On June 28, 1914, the motorcade carrying Austro-Hungarian Archduke Franz Ferdinand and his wife, Sophie, made a wrong turn on the streets of Sarajevo. His car had no reverse gear, so the engine was disengaged and the car pushed back onto the main road. That gave Gavrilo Princip all the time he needed. The 19-year-old Bosnian Serb stepped up to the car and fired twice at point-blank range, fatally wounding both Franz Ferdinand and his wife. “Sophie, Sophie, don’t die. Stay alive for our children,” the heir to the empire said as his helmet, plumed with green ostrich feathers, slipped from his head.

The cataclysmic chain of events that ensued has troubled political and military thinkers to this day. Austria-Hungary made severe demands of Serbia, which it correctly suspected of involvement in the assassinations. Serbia rejected the ultimatum. When Austria-Hungary declared war on Serbia, a web of alliances began to ensnare the entire continent. Russia, as an ally of Serbia, declared it was fully mobilizing its armed forces. Germany, an ally of Austria-Hungary, preemptively declared war first on Russia, then on France, Russia’s ally. The guns of August began to sound. By the time World War I ended in 1918, roughly 17 million combatants and civilians had died, with nothing to show for their loss.

Change 1914 to 2014, and Sarajevo to Homs or Mosul or Donetsk or Kashmir or Panmunjom or the Senkaku Islands or the Spratlys or name-your-own conflict zone. Now as then, fights over small places whose names belong on a quiz show threaten to embroil the world’s most powerful armies. The powder kegs are in place, waiting for a Gavrilo Princip to light the fuse.

What can be done to avoid a recurrence of the Sarajevo Syndrome? The First and Second World Wars offer different lessons. Those of World War I are clear: Keep local conflicts local; communicate; avoid escalation, even if that means letting down a putative ally. World War II has a different moral. The mistake that led to that conflagration was failing to stand up to evil. The haunting image of 1938 is British Prime Minister Neville Chamberlain’s declaration of “peace for our time” upon his return from Munich—having meekly acquiesced in Adolf Hitler’s annexation of German-speaking parts of Czechoslovakia...